U.S. patent application number 09/864229 was filed with the patent office on 2002-01-03 for polishing method and polishing apparatus.
Invention is credited to Isobe, Soichi, Kojima, Hiroshi, Ogura, Suguru, Torii, Hiroomi.
Application Number | 20020002028 09/864229 |
Document ID | / |
Family ID | 18661445 |
Filed Date | 2002-01-03 |
United States Patent
Application |
20020002028 |
Kind Code |
A1 |
Torii, Hiroomi ; et
al. |
January 3, 2002 |
Polishing method and polishing apparatus
Abstract
The present invention relates to a polishing method and
apparatus for polishing a workpiece such as a semiconductor wafer
to a flat mirror finish. A polishing liquid Q is supplied onto a
polishing cloth 11 attached on a turntable 1, and a semiconductor
wafer W to be polished is held by a top ring 2. The turntable 1 and
the top ring 2 are rotated, respectively. A surface, to be
polished, of the semiconductor wafer W held by the top ring 2 is
pressed against the polishing cloth 11 on the turntable 1 to polish
the semiconductor wafer W. When the polished semiconductor wafer W
held by said top ring 2 is to be removed from the polishing cloth
11 on the turntable 1, a relative speed of the turntable 1 and the
top ring 2 is increased in comparison with a relative speed of the
turntable 1 and the top ring 2 at a period of polishing.
Inventors: |
Torii, Hiroomi; (Tokyo,
JP) ; Kojima, Hiroshi; (Tokyo, JP) ; Ogura,
Suguru; (Tokyo, JP) ; Isobe, Soichi; (Tokyo,
JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
18661445 |
Appl. No.: |
09/864229 |
Filed: |
May 25, 2001 |
Current U.S.
Class: |
451/41 |
Current CPC
Class: |
B24B 49/00 20130101;
B24B 37/042 20130101 |
Class at
Publication: |
451/41 |
International
Class: |
B24B 001/00; B24B
007/19 |
Foreign Application Data
Date |
Code |
Application Number |
May 26, 2000 |
JP |
2000-156690 |
Claims
What is claimed is:
1. A polishing method comprising: rotating a turntable having a
polishing surface thereon, and a top ring for holding a workpiece
to be polished, respectively; pressing a surface, to be polished,
of said workpiece held by said top ring against said polishing
surface on said turntable to polish said workpiece; and increasing
a relative speed of said turntable and said top ring when said
polished workpiece held by said top ring is to be removed from said
polishing surface on said turntable, in comparison with a relative
speed of said turntable and said top ring at a period of
polishing.
2. A polishing method according to claim 1, wherein a rotational
speed of said turntable is increased in comparison with a
rotational speed of said turntable at a period of polishing to
increase said relative speed of said turntable and said top
ring.
3. A polishing method according to claim 2, wherein said rotational
speed of said turntable is increased to 100 min.sup.-1 or
larger.
4. A polishing method according to claim 1, wherein rotational
speeds of said turntable and said top ring are respectively
increased in comparison with rotational speeds of said turntable
and said top ring at a period of polishing to increase said
relative speed of said turntable and said top ring.
5. A polishing method according to claim 4, wherein said rotational
speed of said top ring is increased to 75 min.sup.-1 or larger.
6. A polishing method according to claim 5, wherein said rotational
speed of said turntable is increased to 100 min.sup.-1 or
larger.
7. A polishing apparatus for polishing a workpiece to be polished,
comprising: a turntable having a polishing surface thereon; a top
ring for holding said workpiece to be polished and pressing said
workpiece against said polishing surface on said turntable; a motor
for rotating said turntable; and a controller for controlling a
rotational speed of said motor; wherein when said polished
workpiece held by said top ring is to be removed from said
polishing surface on said turntable, said motor increases a
rotational speed of said turntable in comparison with a rotational
speed of said turntable at a period of polishing.
8. A polishing apparatus according to claim 7, wherein said motor
increases said rotational speed of said turntable to 100 min.sup.-1
or larger.
9. A polishing apparatus for polishing a workpiece to be polished,
comprising: a turntable having a polishing surface thereon; a top
ring for holding said workpiece to be polished and pressing said
workpiece against said polishing surface on said turntable; a motor
for rotating said top ring; and a controller for controlling a
rotational speed of said motor; wherein when said polished
workpiece held by said top ring is to be removed from said
polishing surface on said turntable, said motor increases a
rotational speed of said top ring in comparison with a rotational
speed of said top ring at a period of polishing.
10. A polishing apparatus according to claim 9, wherein said motor
increases said rotational speed of said top ring to 75 min.sup.-1
or larger.
11. A polishing method comprising: moving a polishing surface and a
top ring for holding a workpiece to be polished relative to each
other; pressing a surface, to be polished, of said workpiece held
by said top ring against said polishing surface to polish said
workpiece; and increasing a relative speed of said polishing
surface and said top ring when said polished workpiece held by said
top ring is to be removed from said polishing surface, in
comparison with a relative speed of said polishing surface and said
top ring at a period of polishing.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a polishing method and
apparatus, and more particularly to a polishing method and
apparatus for polishing a workpiece such as a semiconductor wafer
to a flat mirror finish.
[0003] 2. Description of the Related Art
[0004] Recent rapid progress in semiconductor device integration
demands smaller and smaller wiring patterns or interconnections and
also narrower spaces between interconnections which connect active
areas. One of the processes available for forming such
interconnection is photolithography. Although the photolithographic
process can form interconnections that are at most 0.5 .mu.m wide,
it requires that surfaces on which pattern images are to be focused
by a stepper be as flat as possible because the depth of focus of
the optical system is relatively small. However, conventional
apparatuses for planarizing semiconductor wafers (substrate-like
workpieces), such as self-planarizing CVD apparatus or etching
apparatus, fail to produce completely planarized surfaces on
semiconductor wafers. Recently, it has been attempted to planarize
semiconductor wafers with a polishing apparatus which is expected
to achieve easily complete planarization of the semiconductor
wafers as compared with the above conventional apparatuses. Such a
process is called Chemical Mechanical Polishing (CMP) in which the
semiconductor wafers are chemically and mechanically polished while
supplying a polishing liquid comprising abrasive particles and
chemical solution such as alkaline solution.
[0005] FIG. 1 is a schematic view showing the basic structure of
this type of polishing apparatus. As shown in FIG. 1, the polishing
apparatus has a turntable 1 with a polishing cloth 11 attached
thereon and constituting a polishing surface, and a top ring 2 for
holding a semiconductor wafer (workpiece) W in such a manner that
the surface, to be polished, of the semiconductor wafer W faces the
turntable 1. The top ring 2 is connected to a lower end of a top
ring shaft 3 via a ball joint 4 so as to be tiltable with respect
to the top ring shaft 3. The semiconductor wafer W to be polished
is pressed against the turntable 1 under a certain pressure by the
top ring 2 while the turntable 1 and the top ring 2 are
independently being rotated, and the surface of the semiconductor
wafer W is polished to a flat mirror finish while a polishing
liquid Q is being supplied from a polishing liquid supply nozzle 5.
In this case, the surface, to be polished, of the semiconductor
wafer W is brought into sliding contact with the upper surface of
the polishing cloth 11 while following the inclination of the upper
surface of the polishing cloth 11 via the ball joint 4.
[0006] As a polishing cloth attached on a turntable, a polishing
cloth made of non-woven fabric has heretofore been employed. Higher
levels of integration achieved in recent years for ICs and LSI
circuits demand smaller steps or surface irregularities on the
polished surface of the semiconductor wafer. In order to meet such
a demand, there has been used a polishing cloth made of a hard
material such as polyurethane foam.
[0007] After the semiconductor wafer W is polished by the polishing
apparatus, it is necessary to remove the semiconductor wafer W from
the polishing surface (the polishing cloth 11 ) on the turntable 1.
However, a large surface tension acts between the polishing cloth
11 and the semiconductor wafer W due to the polishing liquid Q
interposed therebetween. Accordingly, if the top ring 2 holding the
semiconductor wafer W is lifted at the polishing position in order
to remove the semiconductor wafer W from the polishing cloth 11,
there are some cases that only the top ring 2 is lifted and the
semiconductor wafer W adheres to the polishing cloth 11 to be left
on the polishing cloth 11.
[0008] Such a problem can be solved by an overhanging action of the
top ring. In the overhanging action, after the polishing process is
completed, the top ring 2 is not lifted at the polishing position,
but is moved to the outer circumferential edge of the polishing
cloth 11 to partly expose the polished surface of the semiconductor
wafer W beyond the outer circumferential edge of the polishing
cloth 11 and then lifted to remove the semiconductor wafer W from
the polishing cloth 11. This overhanging action allows the surface
tension between the polishing cloth 11 and the semiconductor wafer
W to be reduced, and the semiconductor wafer W can reliably be
separated or removed from the polishing cloth 11.
[0009] As described above, with the overhanging action, the surface
tension between the polishing cloth 11 and the semiconductor wafer
W can be reduced. However, the top ring 2 may tilt when the
polished semiconductor wafer W projects from the outer
circumferential edge of the polishing cloth 11. In this case, the
semiconductor wafer W is intensively pressed at the outer
circumferential edge of the polishing cloth 11, so that the
semiconductor wafer W is cracked or scratched.
[0010] The polishing capability of the polishing cloth is gradually
deteriorated due to a deposit of abrasive particles and ground-off
particles of the semiconductor material, and due to changes in the
characteristics of the polishing cloth. Therefore, if the same
polishing cloth is used to repeatedly polish semiconductor wafers,
the polishing rate of the polishing apparatus is lowered, and the
polished semiconductor wafers tend to suffer polishing
irregularities. Therefore, it has been customary to condition the
polishing cloth according to a process called "dressing" for
recovering the surface of the polishing cloth with a diamond
dresser or the like before, or after, or during polishing.
[0011] When the diamond dresser dresses the polishing surface of
the polishing cloth 11, it scrapes a thin layer off the polishing
cloth 11. Therefore, after the polishing surface of the polishing
cloth has been dressed many times, it becomes irregular, i.e.,
loses its planarity, causing formation of steps. As a result,
during the movement of the polished semiconductor wafer W to the
outer circumferential edge of the polishing cloth 11 in the
aforementioned overhanging action, the semiconductor wafer W may be
cracked or scratched because of the irregularities of the polishing
cloth 11.
SUMMARY OF THE INVENTION
[0012] The present invention has been made in view of the above
drawbacks. It is therefore an object of the present invention to
provide a polishing method and apparatus which can easily and
safely remove a polished workpiece from a polishing surface, and
can increase a throughput.
[0013] According to an aspect of the present invention, there is
provided a polishing method comprising: rotating a turntable having
a polishing surface thereon, and a top ring for holding a workpiece
to be polished, respectively; pressing a surface, to be polished,
of the workpiece held by the top ring against the polishing surface
on the turntable to polish the workpiece; and increasing a relative
speed of the turntable and the top ring when the polished workpiece
held by the top ring is to be removed from the polishing surface on
the turntable, in comparison with a relative speed of the turntable
and the top ring at a period of polishing.
[0014] According to a preferred aspect of the present invention, a
rotational speed of the turntable is increased in comparison with a
rotational speed of the turntable at a period of polishing to
increase the relative speed of the turntable and the top ring.
[0015] According to another preferred aspect of the present
invention, rotational speeds of the turntable and the top ring are
respectively increased in comparison with rotational speeds of the
turntable and the top ring at a period of polishing to increase the
relative speed of the turntable and the top ring.
[0016] According to another aspect of the present invention, there
is provided a polishing apparatus for polishing a workpiece to be
polished, comprising: a turntable having a polishing surface
thereon; a top ring for holding the workpiece to be polished and
pressing the workpiece against the polishing surface on the
turntable; a motor for rotating the turntable; and a controller for
controlling a rotational speed of the motor; wherein when the
polished workpiece held by the top ring is to be removed from the
polishing surface on the turntable, the motor increases a
rotational speed of the turntable in comparison with a rotational
speed of the turntable at a period of polishing.
[0017] According to still another aspect of the present invention,
there is provided a polishing apparatus for polishing a workpiece
to be polished, comprising: a turntable having a polishing surface
thereon; a top ring for holding the workpiece to be polished and
pressing the workpiece against the polishing surface on the
turntable; a motor for rotating the top ring; and a controller for
controlling a rotational speed of the motor; wherein when the
polished workpiece held by the top ring is to be removed from the
polishing surface on the turntable, the motor increases a
rotational speed of the top ring in comparison with a rotational
speed of the top ring at a period of polishing.
[0018] According to another aspect of the present invention, there
is provided a polishing method comprising: moving a polishing
surface and a top ring for holding a workpiece to be polished
relative to each other; pressing a surface, to be polished, of the
workpiece held by the top ring against the polishing surface to
polish the workpiece; and increasing a relative speed of the
polishing surface and the top ring when the polished workpiece held
by the top ring is to be removed from the polishing surface, in
comparison with a relative speed of the polishing surface and the
top ring at a period of polishing.
[0019] It is desirable that the rotational speed of the turntable
be increased to 100 min.sup.-1 or larger, and the rotational speed
of the top ring be increased to 75 min.sup.-1 or larger.
[0020] According to the present invention, the liquid film
thickness of a polishing liquid on the polishing surface is
decreased by the action of the centrifugal force, so that the
surface tension due to the polishing liquid is reduced. Therefore,
even if the top ring is lifted at the polishing position without an
overhanging action, the workpiece can easily be removed from the
polishing surface. Thus, the present invention can prevent the
workpiece from being left on the polishing surface and being
cracked or scratched. Further, since it is not necessary to perform
the overhanging action, tact time for polishing can be reduced to
increase a throughput. Furthermore, when the rotational speed of
the turntable is increased, the components of the polishing liquid
are scattered and discharged from the upper surface of the
turntable by the action of the centrifugal force. Accordingly, it
becomes easier to remove the workpiece from the polishing surface,
and simultaneously the polishing conditions for the next workpiece
to be polished can be arranged to be preferred conditions. As a
result, the throughput can be increased.
[0021] The above and other objects, features, and advantages of the
present invention will be apparent from the following description
when taken in conjunction with the accompanying drawings which
illustrates preferred embodiments of the present invention by way
of example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a schematic view showing the basic structure of a
polishing apparatus;
[0023] FIG. 2 is a front view showing the whole structure of a
polishing apparatus according to an embodiment of the present
invention; and
[0024] FIG. 3 is a schematic view showing a mechanism for vacuum
attraction of a wafer according to an embodiment of the present
invention;
[0025] FIGS. 4A and 4B are schematic views showing an overhanging
action; and
[0026] FIG. 5 is a schematic view showing a polishing apparatus
according to another embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] A polishing method and apparatus according to an embodiment
of the present invention will be described below with reference to
FIG. 2. FIG. 2 is a front view showing the whole structure of a
polishing apparatus according to an embodiment of the present
invention. In FIG. 2, like parts and components are designated by
the same reference numerals and characters as those shown in FIG.
1.
[0028] As shown in FIG. 2, the polishing apparatus according to the
present embodiment comprises a turntable 1, a polishing liquid
supply nozzle 5, and a top ring unit 6. The turntable 1 has a
vertical shaft 13 coupled to a motor 12 disposed below the
turntable 1 and is rotatable about the shaft 13, as indicated by an
arrow in FIG. 1. The motor 12 is connected to a controller 14 for
controlling a rotational speed of the motor 12. A polishing cloth
11 is attached on an upper surface of the turntable 1. The
polishing cloth 11 has an upper polishing surface held in sliding
contact with a semiconductor wafer W (workpiece) to be polished.
The polishing liquid supply nozzle 5 is disposed above the
turntable 1, and a polishing liquid Q is supplied onto the
polishing cloth 11 of the turntable 1 from the polishing liquid
supply nozzle 5.
[0029] In the present embodiment, as described above, the turntable
1 has the polishing cloth 11 attached thereon. However, the
turntable 1 is not limited to the above one, and the turntable 1
may comprise a polishing plate of a fixed abrasive, for example.
The fixed abrasive comprises abrasive particles fixed by a
binder.
[0030] As shown in FIG. 2, the top ring unit 6 mainly comprises a
swing shaft 61, an arm-shaped top ring head 62 connected to the
swing shaft 61, and a top ring 2 connected to a top ring shaft 3
extended downwardly from the top ring head 62. The top ring head 62
is swingable in a horizontal plane by rotation of the swing shaft
61. The top ring 2 is connected to the lower end of the top ring
shaft 3 via a ball joint 4 so as to be tiltable with respect to the
top ring shaft 3.
[0031] The top ring 2 of the top ring unit 6 has, on a lower
surface thereof, an elastic pad 21 formed of polyurethane or the
like. The semiconductor wafer W is attracted to a lower surface of
the elastic pad 21 under a vacuum in such a state that the
semiconductor wafer W is brought into contact with the lower
surface of the elastic pad 21, so that the semiconductor wafer W is
held by the top ring 2. The top ring 2 has a cylindrical guide ring
22 at an outer circumferential edge of a lower portion thereof. A
lower portion of the guide ring 22 protrudes from the top ring 2,
and hence a recess is formed at the radially inner side of the
lower portion of the guide ring 22. The semiconductor wafer W is
held in the recess for preventing the semiconductor wafer W from
being dislodged from the lower surface of the top ring 2 during the
polishing process.
[0032] The top ring 2 is coupled to a motor 63 provided in the top
ring head 62 via the top ring shaft 3, and is rotatable about the
top ring shaft 3. The motor 63 is connected to a controller 63 a
for controlling a rotational speed of the motor 63. The top ring 2
is also coupled to a lifting/lowering cylinder 64 via the top ring
shaft 3, and is vertically movable for pressing the semiconductor
wafer W held in the top ring 2 against the polishing cloth 11 under
a predetermined pressure.
[0033] In the polishing apparatus thus constructed, the
semiconductor wafer W held on the lower surface of the elastic pad
21 attached on the lower surface of the top ring 2 is pressed
against the polishing cloth 11 on the turntable 1, while the
polishing liquid Q is being supplied onto the polishing cloth 11 of
the turntable 1 from the polishing liquid supply nozzle 5. The
turntable 1 and the top ring 2 are independently rotated, so that
the polishing cloth 11 and the semiconductor wafer W are moved
relative to each other. For example, a suspension of fine polishing
particles of silica or the like in an alkali solution is used as
the polishing liquid supplied from the polishing liquid nozzle 5.
Thus, the semiconductor wafer W is polished to a flat mirror finish
by the combined effect of a chemical polishing effect attained by
the alkali and a mechanical polishing effect attained by the
polishing particles.
[0034] The semiconductor wafer W is polished in the above manner.
After the polishing process of the semiconductor wafer W is
completed, it is necessary to separate or remove the semiconductor
wafer W from the polishing cloth 11 on the turntable 1. In this
case, the surface tension acts between the polishing cloth 11 and
the semiconductor wafer W, as described above. According to the
present invention, when the semiconductor wafer W is to be
separated or removed from the polishing cloth 11, the rotational
speeds of the turntable 1 and the top ring 2 are increased by the
motor 12 and the motor 63 in comparison with their rotational
speeds at a period of the polishing process. As a result, reduction
of the surface tension can be achieved as follows:
[0035] Specifically, when the rotational speeds of the turntable 1
and the top ring 2 are increased, the liquid film thickness of the
polishing liquid Q on the polishing cloth 11 is decreased by the
action of the centrifugal force, so that the surface tension due to
the polishing liquid Q is reduced. Therefore, even if the top ring
2 is lifted at the polishing position without an overhanging
action, the semiconductor wafer W can easily be removed from the
polishing cloth 11. Thus, the present invention can prevent the
semiconductor wafer W from being left on the polishing cloth 11 and
being cracked or scratched. Further, since it is not necessary to
perform the overhanging action, tact time for polishing can be
reduced to increase a throughput. Furthermore, when the rotational
speed of the turntable 1 is increased by the motor 12, the
components of the polishing liquid are scattered and discharged
from the upper surface of the turntable 1 by the action of the
centrifugal force. Accordingly, it becomes easier to remove the
semiconductor wafer from the polishing surface, and simultaneously
the polishing conditions for the next semiconductor wafer to be
polished can be arranged to be preferred conditions. As a result,
the throughput can be increased.
[0036] In the present embodiment, as shown in FIG. 3, a vacuum line
8 communicating with a vacuum evacuation source 7 is connected to
the top ring 2. The top ring 2 has a chamber (or a space) 2a
connected to the vacuum line 8, and a plurality of holes 2b
communicating with the chamber 2a and being open to the lower
surface of the top ring 2. Thus, the semiconductor wafer W is held
on the lower surface of the top ring 2 by vacuum attraction. When
the semiconductor wafer W is to be removed from the polishing cloth
11, the top ring 2 is mechanically lifted. If the semiconductor
wafer w is dislodged from the top ring 2 and is left on the
polishing cloth 11, the pressure of the vacuum line 8 changes from
a vacuum nearer to the atmospheric pressure. Therefore, the
pressure of the vacuum line 8 is monitored to judge whether the
semiconductor wafer W has normally been removed from the polishing
cloth 11 or not.
[0037] In the present embodiment, as shown in FIG. 3, a vacuum
pressure sensor 9 is provided in the vacuum line 8 to measure and
monitor the pressure of the vacuum line 8, for thereby judging
whether the semiconductor wafer W has normally been removed from
the polishing cloth 11 or not. Specifically, after the lifting
operation of the top ring 2 is started, the pressure of the vacuum
line 8 is measured with the vacuum pressure sensor 9. If the
measured value is less than a predetermined pressure value, it is
judged that the semiconductor wafer W has normally been removed
from the polishing cloth 11 in such a state that the semiconductor
wafer W is attracted to the top ring 2. More specifically, if
pressures that are 10 kPa or more larger than the predetermined
pressure value, at which the semiconductor wafer W is judged to be
normally attracted to the top ring 2, are measured for a
predetermined period or longer, then it is judged that the
semiconductor wafer W has been dislodged from the top ring 2.
[0038] Experiments were carried out as follows:
[0039] A strain gauge was provided in the top ring, and the
rotational speeds of the turntable and the top ring were
respectively changed when the semiconductor wafer was to be removed
from the polishing cloth. An axial force acting on the top ring at
this time, i.e., a force for lifting the top ring, was
measured.
[0040] A top ring for holding a semiconductor wafer having a
diameter of 200 mm was used.
[0041] Dressing was performed for 600 seconds by a dresser before a
polishing process.
[0042] After three semiconductor wafers were polished as dummies to
obtain the normal condition of the polishing cloth, two
semiconductor wafers were polished for measuring a force for
lifting the top ring. The force for lifting the top ring was
calculated based on the average of the values measured after
polishing of the two semiconductor wafers.
[0043] During the polishing process, the rotational speed of the
turntable was 22 min.sup.-1, and the rotational speed of the top
ring was 16 min.sup.-1.
[0044] When the semiconductor wafer was lifted, the rotational
speed of the turntable was changed to 50 min.sup.-1, 75 min.sup.-1
or 100 min.sup.-1, and the rotational speed of the top ring was
changed to 55 min.sup.-1 or 75 min.sup.-1.
[0045] As the dresser, a new dresser and a used dresser that had
already used for processing 17,000 semiconductor wafers were used
in the experiments, respectively.
[0046] The measurement results in the above experiments are shown
in Table 1.
1 TABLE 1 Force for Force for Rotational lifting top lifting top
speed of Rotational ring in the ring in the turntable speed of top
case of new case of used (min.sup.-1) ring (min.sup.-1) dresser (N)
dresser (N) 50 55 332.1 342 75 55 99.9 378.9 100 55 378 185.4 50 75
389.7 300.9 75 75 338.7 178.8 100 75 25.9 96.6
[0047] From Table 1, it is shown that, in both cases of the new
dresser and the used dresser, when the rotational speed of the
turntable and the rotational speed of the top ring at a period of
lifting a semiconductor wafer were the largest, i.e., when the
rotational speed of the turntable was 100 min.sup.-1, and the
rotational speed of the top ring 75 min.sup.-1, the force for
lifting the top ring was the lowest. In this case, the
semiconductor wafer W could easily be lifted from the polishing
cloth 11.
[0048] In the present embodiment, the top ring 2 is lifted at the
polishing position without an overhanging action. However, the top
ring 2 may perform an overhanging action after the polishing
process, as shown in FIGS. 4A and 4B. After the polishing process
is completed, the top ring 2 is moved to the outer circumferential
edge of the polishing cloth 11 to partly expose the polished
surface of the semiconductor wafer W beyond the outer
circumferential edge of the polishing cloth 11 and then lifted to
remove the semiconductor wafer W from the polishing cloth 11. When
the semiconductor wafer W is to be separated or removed from the
polishing cloth 11, the rotational speed of the top ring 2 is
increased in comparison with the rotational speed at a period of
the polishing process. The liquid film thickness of the polishing
liquid on the polishing cloth 11 is decreased by the action of the
centrifugal force, so that the surface tension due to the polishing
liquid is reduced by the synergistic effect of the centrifugal
force and the overhanging action. Therefore, the semiconductor
wafer W can more easily be removed from the polishing surface. As a
result, the semiconductor wafer W can be prevented from being left
on the polishing surface 18 more effectively.
[0049] In the present embodiment, the polishing surface is rotated
to polish the semiconductor wafer. However, the polishing surface
and the top ring may be moved relative to each other. In FIG. 5, a
polishing surface is constituted by a belt 15 having abrasive
particles on its surface. The belt 15 is wound on two rotatable
drums 16, 17. The drums 16, 17 are rotated to linearly move the
belt 15 along an arrow A. A support 18 is disposed between an upper
belt surface 15a and a lower belt surface 15b. A semiconductor
wafer held by the top ring 2 is pressed against the belt 15 and the
support 18. Thus, the semiconductor wafer is polished. When the
semiconductor wafer is to be separated or removed from the belt 15,
the rotational speed of the top ring 2 is increased in comparison
with the rotational speed at a period of the polishing process. As
in the case of the aforementioned embodiment, the semiconductor
wafer can be prevented from being left on the belt 15 (polishing
surface).
[0050] As described above, according to the present invention, when
a polished workpiece held by a top ring is to be removed from a
polishing surface on a turntable, a rotational speed of the
turntable is increased in comparison with a rotational speed of the
turntable at a period of polishing. A relative speed of the
turntable and the top ring is increased in comparison with a
relative speed of the turntable and the top ring at a period of
polishing. Hence, even if the top ring is lifted at the polishing
position without an overhanging action, the workpiece can easily be
removed from the polishing surface. Thus, the present invention can
prevent the workpiece from being left on the polishing surface and
being cracked or scratched. Further, since it is not necessary to
perform the overhanging action, tact time for polishing can be
reduced to increase a throughput. Furthermore, when the rotational
speed of the turntable is increased, the components of the
polishing liquid are scattered and discharged from the upper
surface of the turntable by the action of the centrifugal force.
Accordingly, it becomes easier to remove the workpiece from the
polishing surface, and simultaneously the polishing conditions for
the next workpiece to be polished can be arranged to be preferred
conditions. As a result, the throughput can be increased.
[0051] Although certain preferred embodiments of the present
invention have been shown and described in detail, it should be
understood that various changes and modifications may be made
therein without departing from the scope of the appended
claims.
* * * * *